Full moon in South Iceland with halo and high intensity spots of light.

Wolves chasing the Easter moon

3.4.2008

On the eve of Good Friday, 21st March, an unusual phenomenon was seen in the night sky: The full moon had a halo with bright spots on either side. Such high intensity spots are common on haloes around the sun (parhelia or sundogs), but they are rarely seen around the moon (paraselenae or moondogs).

The reason for the halo was a thin veil of cirrus or cirrostratus clouds at high altitude, made of of hexagonal ice crystals that refract the light. Both in Norse and Greek mythology, the spots are described as wolves, chasing the sun and the moon.